1. Field of the Invention
the present invention relates to a method of adjusting the position of each lens group provided in a zoom lens and to a zoom lens utilizing the result of such adjustment.
2. Description of Background Information
A conventional zoom lens which includes two or three lens groups is generally provided with a cam mechanism for moving the focal length-varying lens groups in a predetermined relationship to vary magnification. In such a conventional zoom lens, a focusing lens group, which may also serve as one of the focal length-varying lens groups, is driven to bring an object into focus.
In such a conventional zoom lens provided with a cam mechanism, each lens group is steadily driven according to the profile of the cam mechanism. However, it is practically impossible to accurately correct the positional error of each movable lens group occurred at the time of manufacture or assembly of the zoom lens Furthermore, in such a conventional zoom lens, a cam having cam edges or grooves with complicated contours needs to be provided, which results in a high production cost. In addition, the zoom lens needs to have sufficient space for positioning the cam mechanism inside the zoom lens, which makes it difficult to miniaturize the zoom lens.
In order to overcome the aforementioned problems that occur upon utilizing a cam, there has been proposed a mechanism for zooming in which the focal length varying lens groups and the focusing lens group are each independently driven relative to each other. In this case, position of each focal length-varying lens group which varies due to a zooming operation and the position of the focusing lens group which varies in accordance with an object distance are given through a predetermined calculation. Further, for each of a plurality of focal lengths of the zoom lens, the corresponding position of the focusing lens group with reference to a specific position thereof at which the zoom lens is focused on an object at infinity is calculated and is stored in advance as positional data in a storing device such as a ROM. Subsequently, after the focal length-varying lens group(s) is driven to vary the magnification, the stored positional data of the focusing lens group for the current position(s) of the focal length-varying lens group(s) is read from the ROM and the focusing lens group moves to the position corresponding to the read positional data. Such a zooming mechanism has been proposed in, for example, Japanese Patent Application No.7-172216.
For such a zoom lens (including a vari-focal lens) position at relationship of the focal length-varying lens group and the focusing lens group of the zoom lens often deviate from the designed positions due to error originated in the manufacturing and/or assembling process, or change of temperature. Accordingly, in order to eliminate the deviation as above described, a zooming adjustment and a focus adjustment should be carried out. When zooming adjustment is carried out, the position of each focal length-varying lens group of the zoom lens is adjusted so that an appropriate in-focus state can be obtained at a plurality of focal lengths, including at least the shortest focal length and the longest focal length. The focus adjustment is carried out after the zooming adjustment is completed. During focus adjustment, the focus point of the zoom lens is adjusted so as to coincide with a reference focal plane, namely an image plane such as a film plane or the light receiving surface of an image pick-up device (CCD), etc. Therefore, there has been a strong need for means a for detecting such error and for correcting the same.
With the above mentioned zoom lens problems taken into consideration, it is the object of the present invention to provide a zoom lens adjusting method of which the focal length and the lens position can be easily adjusted, and wherein it is possible for the focal length varying lens group and the focusing lens group to be freely designed.
Another object of the present invention is to provide a zoom lens in which the above-mentioned adjusting method can be carried out during zoom operation according to adjustment data obtained by the above method of adjusting.